1. Field of the Invention
The present invention concerns transmission lubrication systems and, more particularly, transmission lubrication cooling systems.
2. Description of Related Art
Several vehicle transmission lubrication circuits are known in the art. A first known system is illustrated in FIG. 1, and generally includes a pump 10, a torque converter 12, a shifting control assembly 14, a shaft lubrication (lube) assembly 16, an oil cooler 18, and a sump 20. During normal operation of this system, about eighty percent of the lubricating fluid is directed through the shifting control assembly 14, while about twenty percent of the lubricating fluid is directed through the torque converter 12, shaft lube assembly 16, and oil cooler 18.
The torque converter 12 may either be operated in a lock-up mode or in a non-lockup mode, with the non-lockup mode being referred to hereinafter as normal operation. During normal operation of such transmissions, the torque converter 12 is a primary source of heat generation, while lubricated shafts 16 are secondary sources of heat generation. During operation of the torque converter 12 in a lock-up mode, the torque converter no longer generates heat, but still has a significant amount of residual or built-up heat that must be dissipated. However, the lubricated shafts 16 continue to generate heat that must be dissipated. In the system illustrated in FIG. 1, since all of fluid flowing through the torque converter 12 and shafts 16 passes through the cooler before returning to the sump 20, heat build up is generally not a problem. However, since most of the lubricating fluid is provided to the torque converter 12, the pump 10 may have to be increased in capacity in order to provide adequate lubrication of the shafts 16.
An alternative known transmission lubricating circuit is generally shown in FIG. 2, and includes many of the same components as shown in FIG. 1. However, in FIG. 2 the lubrication of the transmission shafts is split into different lubricating paths. Moreover, during normal operation of the lubricating circuit shown in FIG. 2, about eighty percent of fluid is directed through or over the shifting control 14 and transmission shafts 16, while only about twenty percent of lubricating fluid flow is through the torque converter 12.
Generally, when the torque converter of the lubricating circuit of FIG. 2 is operating normally, pressurized lubricating oil from the pump may be considered as being split into three separate lubricating flows. A first flow {circle around (1)} goes through the torque converter 12, a second flow {circle around (2)} goes through the shift control structure 14, and a third flow {circle around (3)} goes through the main, secondary, and counter shafts 16. The first flow, after passing through the torque converter 12, passes through the oil cooler 18 before returning to the sump 20. On the other hand, the second and third flows, after passing over and/or through the associated transmission components 14, 16, return directly to the sump 20.
More specifically, and with reference to FIG. 3, the first flow {circle around (1)} is directed through a regulator valve 22, a lockup shift valve 24 and, ultimately to the torque converter 12. The second flow {circle around (2)} is directed to the shifting control structure 14 of the transmission. The third flow {circle around (3)} splits off of the first flow at the regulator valve 22, and directs the lubricating fluid to the main, secondary, and counter shafts 16 of the transmission. More specifically, the third flow of oil is directed to a pressure tap 26, and splits into a first portion 28 and a second portion 30. The first portion 28 is provided to the main shaft 32, while the second portion 30 flows through a lube check valve 34 to the secondary shaft 36 and the counter shaft 38. The lube check valve 34 serves to limit flow to the shafts 36, 38 when lubricating fluid is cold to prevent creep in neutral.
With regard to the first flow {circle around (1)}, the lubricating fluid is heated in the torque converter 12, and exits via two paths 40, 42 therefrom, each of which eventually lead to the sump 20 via the oil cooler 18. The oil in the first path 40 flows through a torque converter check valve 44 and then to the oil cooler 18, while the oil in the second path 42 flows back through the torque converter lockup shift valve 24, and then to the oil cooler 18. From the oil cooler 18, the cooled lubricating fluid goes through an oil filter 46 and then into the sump 20. From the sump 20, the oil, only a part of which has been cooled, is provided to the pump 10 and recirculated through the lubricating and cooling circuit.
When the torque converter 12 locks up, such as during normal cruising, the first flow path changes, while the second and third flow paths remain unchanged. More specifically, the lockup control valve 48, torque converter shift valve 24, and torque converter lockup timing valve 50 shift positions, and the transmission oil flows through the torque converter shift valve 24 to the torque converter 12, as shown by the arrow labeled {circle around (4)}. However, essentially only one outlet is provided for the oil from the torque converter 12, and oil flows through the single outlet (first path 40), through the torque converter check valve 44, to the oil cooler 18.
The aforementioned system works satisfactorily during normal operation of the transmission. However, during lockup of the torque converter 12 the lubricating oil flow through the torque converter 12, and ultimately through the oil cooler 18, is reduced. This reduction in flow causes the temperature of the oil to increase. In extreme situations, the viscosity of the oil is increased to a level that the oil begins to boil, and may leak from the transmission seals, especially at the second and counter shafts 36, 38. Accordingly, in the prior art transmission oil cooling circuit illustrated in FIGS. 2 and 3, it is sometimes necessary to provide a secondary or supplemental transmission oil cooling circuit when towing is contemplated. Naturally, such supplemental cooling circuits are expensive, and introduce further concerns, such as space concerns, and are generally to be avoided.
Accordingly, there exists a need in the art for an improved or modified transmission oil cooling circuit that eliminates the need for supplemental oil cooling. There further exists a need in the art for an improved transmission oil cooling circuit wherein cooling oil from further heat-generating components is directed through the oil cooler.